On the contribution of cosmic-ray interactions in the circumgalactic gas to the observed high-energy neutrino flux

TL;DR

This paper investigates the potential contribution of cosmic-ray interactions in the circumgalactic gas to the high-energy neutrino flux observed by IceCube, finding it to be subdominant under various assumptions.

Contribution

It provides a comprehensive re-evaluation of the diffuse neutrino flux from cosmic-ray interactions in the circumgalactic medium, considering different cosmic-ray spectra and propagation models.

Findings

The neutrino flux from circumgalactic interactions is subleading compared to observations.

Multimessenger constraints limit the maximum contribution of this process.

Different cosmic-ray models do not significantly change the subdominant nature of this flux.

Abstract

Cosmic rays escaping the Milky-Way disk interact with circumgalactic gas which fills the virial volume of our Galaxy. These interactions should produce guaranteed fluxes of energetic diffuse neutrinos and photons observable at the Earth. This neutrino flux would be a plausible contribution to the spectrum measured by the IceCube neutrino observatory: the energy emitted in this way is weakly constrained from cascade gamma rays, since the cascades have no time to develop, but the arrival directions of the neutrinos do not point to the Galactic disk, in agreement with observations. However, previous studies reported very different estimates of the corresponding neutrino flux, so it was unclear if this contribution to the observed spectrum is essential. Here we readdress the calculation of this diffuse neutrino flux component under various assumptions about the cosmic-ray spectrum and propagation in the circumgalactic medium. We find that even with these variations, this contribution to the observed neutrino flux remains subleading provided multimessenger constraints are satisfied.